2Checkout is the most popular payment gateway which can accept payments in 197 countries via credit and debit cards. With the help of this addon, you can accept donations via credit cards. It has support for 87 currencies and comes with advanced fraud protection. It is well documented and has seamless integration within few minutes.
Constant Contact is a great service for email marketing. Integrating the Constant Contact to your website creates a powerful combo which allows you to set global and per-form settings for various subscription options. You can add donors to any specific mailing list to can set a global list. This plugin provides hastle free integration with Constant Contact services.